Implantable medical devices typically have a housing generally designated as the “generator”, which is electrically and mechanically connected to one or more intracorporeal “leads” provided with electrodes that are intended to come into contact with the patient's tissues on which it is desired to apply the aforementioned electrical pulses and/or collect an electrical signal: e.g., the myocardium, nerve, or muscle tissue.
The current principle of electrical stimulation of tissue (hereinafter, stimulation is used in its generic sense of delivering an energy pulse to tissue rather than in a context of delivering an energy pulse suitable for pacing) is based on a device, usually called a “lead”, which is an object implanted through various venous, arterial or lymphatic vessels, and whose function is to transmit an electrical signal between a generator at a proximal end of the lead target and a tissue at a distal end of the lead while ensuring the following properties:                Ease of implantation by the physician in a vessel network of the patient, and especially ease of advancing the lead into the vessel(s) by pressure, to make the lead follow the tortuous paths and passing side branches in the vessel network, and to transmit torques from one end of the lead to the other;        Detectable by X-rays to allow the doctor to easily navigate through the network of vessels guided by X-ray fluoroscopy;        Atraumaticity of the lead in the veins, which requires a flexible structure and the lack of a rigid transition or sharp edges;        Ability to transmit an electrical signal to tissues and to make stable monopolar or multipolar electrical measurements;        Biocompatibility with living tissue for implantation in the long term;        Ability to connect to an implantable device generator or other source of electrical signals to be transmitted;        Ability to be sterilized (e.g., by gamma radiation, temperature . . . ) without damage;        Biostability, especially corrosion resistance in the living environment and resistance to mechanical fatigue stress related to patient and organs movement;        Compatibility with magnetic resonance imaging (MRI) which is, particularly important in neurology.        
The current architecture of leads that meet these needs can be summarized as a generally hollow structure that allows passage of a stylet or a guidewire, and includes components such as insulated current carrying conducting cables or “lines”, connected to mechanical electrodes for ensuring electrical conductivity, radiopacity, etc. These leads therefore require a complex assembly of a large number of parts, of associated wires and insulating elements, creating substantial risks of rupture given the long-term mechanical stresses they face.
Examples of such known leads are given in U.S. Pat. Nos. 5,246,014, 6,192,280, and 7,047,082.
One of the challenges in making suitable leads includes the management of stiffness gradients related to the mechanical components used, which strongly affect the implantability of the lead and its long term strength (fatigue endurance) properties.
In addition, to seal the inner lumen of the leads, for which the blood would degrade the performance during implantation and in the long term, valves and other complex devices are used, with significant associated risks.
Other difficulties may also arise in terms of fatigue of the assemblies. Indeed, any stiffness in a transition area is likely to induce a risk of fatigue, difficulty in sterilization because of the presence of areas that are difficult to access, and problems of mechanical strength at junctions of the conductors with the distal electrodes and with the proximal connector to the generator.
Moreover, the clinical trend in the field of implantable leads is to reduce their size to make them less invasive and easier to handle through the vessels.
The current size of implantable leads is typically on the order of 4 to 6 French (1.33 to 2 mm) in their active part, that is to say, the most distal end bearing the electrode(s)—even if the lead body, in the less distal end, uses conductors with a smaller diameter, for example, as described in U.S. Pat. No. 5,246,014 above, which, at the lead body, certainly includes a conductor the diameter of which does not exceed 1 French (0.33 mm), but the overall diameter of the distal end active part at the location of the screw anchor is several French. However, it is clear that reducing the size of the leads would increase their complexity and impose technical constraints generating risks.
On the other hand, such a reduction, to less than 2 French (0.66 mm), for example, would open up prospects for medical applications in various fields ranging from cardiology to neurology in the presence of a venous, arterial or lymphatic system such as the cerebral venous system or the coronary sinus venous system.
Today, the electrical stimulation technology has led to major advances in the field of neuromodulation and stimulating target areas of the brain to treat Parkinson's disease, epilepsy and other neurological diseases. One could imagine implementing this type of technology to address new areas difficult to reach today, by using small size stimulation leads, or “microleads”, having great strength to ensure long-term biostability. Such a technique would allow a less invasive approach to these therapies and an especially superior efficacy of treatments.
It would be possible to connect one or more microleads through the considered vessel network until the target location. Their implantation could be done, because of their small size, by today's guiding devices used in interventional neuro-radiology for the release of stents (spring coils) in the treatment of intracranial aneurysms.